This invention relates to an electronic controller for controlling an automatic transmission with fail-safe control functions provided to cope with malfunctions of a controller circuit for driving an actuator such as a solenoid.
Ordinarily, in electronically controlled automatic transmissions, solenoids are used as actuators for shifting, lock-up clutch operation, pressure regulation, and similar operations. If a malfunction of such solenoids due to disconnection or a short circuit takes place, the electronic controller controls the transmission so as to avoid considerable failure in the running of the vehicle.
The arrangement of an electronic controller of this kind will be described below with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram of the construction of a conventional electronic automatic transmission controller of this kind.
As shown in FIG. 1, an electronic controller 1 is constituted by a microcomputer 2, a first driving circuit 3 for driving a first solenoid 8, a first monitor circuit 4 for observing the first solenoid 8, a second driving circuit 5 for driving a second solenoid 9, and a second monitor circuit 6 for observing the second solenoid 9.
FIG. 2 shows an example described below of the circuit arrangement corresponding to that shown in FIG. 1.
A solenoid driving circuit 20 is constituted by a switching p-n-p transistor (TR1) 21, resistors 22, 23, 25 26, and 27, an n-p-n transistor 24, a negative logic NOT circuit 28, and a diode 29. A monitor circuit 30 is constituted by resistors 31 and 32, and a positive logic NOT circuit 33. A battery 50 provided as a power source is connected to a point E for connection to the emitter of the TR1 of the solenoid driving circuit 20. A solenoid 52 is connected at its one end to the ground and at its other end to a point C for connection to the collector of the TR1. Similarly, a solenoid driving circuit 60 for driving a solenoid 53 and a monitor circuit 70 for observing this solenoid are provided.
It is possible to manufacture this controller in full consideration of improvement in the reliability of the switching device as well as wiring while adopting suitable measures for attaining safety with respect to mechanisms. However, it is difficult for this controller to effect desired control if an abnormality such as a short circuit of the switching device takes place. A further improvement in controllers of this kind is therefore expected.